The present invention relates to a rolling method for a strip rolling mill and to a strip rolling facility or equipment.
When a strip is rolled, the strip thickness is distributed non-uniformly in a strip width direction. In a conventional four-high rolling mill in particular, there occur a so-called edge drop in which the thickness decreases sharply at the width ends of the strip, resulting in degrading a quality of and lowering yields of a rolled product.
In view of this problem, there has been a demand for a technology for changing a strip thickness distribution over the entire width and for reducing the edge drop. Examples of such a technology concerning a six-high rolling mill are disclosed in JP-59-18127B, JP-50-45761A, and Nisshin Seiko Technical Report No. 79 (1999), pp 47–48.
Other examples include JP-60-51921B, JP-08-192213A, JP-61-126903A, JP-03-51481A, JP-11-123407A and JP-10-76301A.
During the process of rolling a strip, the amount of edge drop varies even when the strip width is constant. The reason for this is that a profile of the material, its hardness distribution, a rolling load and an amount of roll heat expansion vary during rolling and thus change the amount of edge drop. The present applicants have found that moving a work roll in the axial direction during rolling to minimize these changes results in grave defects in the surface of the material being rolled.
This surface defect problem is particularly more serious with a reversible rolling mill which uses one or a small number of stands and performs multiple rolling passes by reversing the rolling direction than with a tandem mill that uses a plurality of rolling mills and performs a rolling operation in only one direction.